Diatom and macroinvertebrate communities dynamic: A co-occurrence pattern analysis on plastic substrates.

Wetlands are habitats that provide numerous ecosystem services, but are often understudied and threatened by anthropogenic pollution, particularly plastic pollution. Macroplastics are a significant component of plastic litter that have high biological impacts but are often understudied. Previous studies have highlighted negative impacts on biota, but there is a lack of information about the communities of micro and macro organisms that settle on macroplastic litter. In this context, we investigated the colonization patterns and community structures of diatoms and macroinvertebrates on virgin substrates composed of two different plastic polymers, polystyrene and polyethylene terephthalate, located at two different depths in a protected wetland in Central Italy over a period of 10 months. The results show that diatom community is not highly structured by competitive forces and aggregation patterns emerges. In contrast, macroinvertebrate community appears to be randomly structured, without the presence of patterns following specific assembly rules. Randomness in macroinvertebrates assemblages could highlight the presence of different niches available for settlement of different taxa. Combined matrix analyses show that diatoms and macroinvertebrates co-occur, and their community assemblages are sometimes structured, while they appeared to be randomly assembled at other times. Whenever non-randomness of diatoms and macroinvertebrates co-occurrences was detected, it suggested aggregation. Moreover, the possible predatory relationship between different macroinvertebrates taxa should be investigated, as it could reveal important scenarios in the establishment of macroinvertebrate structured communities on plastic litter, including taxa that exploit different ecological niches. This could lead to an enrichment of the biological community within areas impacted by plastics.